PCHPI Project Summary Essentially every step in the HIV life cycle interfaces intimately with the host cell machinery. The Pittsburgh Center of HIV Protein Interactions focuses on the steps and interactions that occur with the host after engagement of cell surface receptors and membrane fusion through integration of the viral genome into that of the host, the so called ?early events?. Several essential molecular interactions and enzymatic activities occur within this time window, necessary for productive progression of the viral life cycle. Thus, it represents a pivotal period in the infection process, during which the susceptibility of the virus to disruptive interventions is likely to be high and little explored. Broadly speaking, the processes that we focus on include uncoating (the process by which the capsid disassembles), reverse transcription, evasion from innate immune factors, nuclear entry and integration. Given the importance of the capsid structure and its interactions for many of these processes, we also explore maturation and in particular formation of the capsid core. We are building on our successes and applying the extensive and complementary experimental expertise of our team to carry out 1) biochemical and high-resolution structure studies of individual proteins and complexes, 2) biochemical, biophysical, and proteomics analyses to identify novel interactions and complexes, 3) virology and imaging studies to understand protein function in the context of the cell and virus infection, and 4) computational analyses to elucidate the physical basis of capsid formation and capsid interactions with binding partners. Broadly, the program comprises projects on capsid interactions, the engagement of Vpr with the DNA repair machinery, and retroviral intasome structure. The requested administrative supplement will provide funds for the purchase of a differential scanning calorimeter, instrumentation essential for continued rigor in our protein production and characterization pipeline toward high-resolution structures of HIV-host protein complexes. Relevance Results provided by the proposed research are expected to have major implications in the global fight against AIDS, still considered an incurable disease with a pressing need for new therapeutic strategies and novel drug targets. Identifying and characterizing atomic structures of key HIV-1 host protein interactions in the immediate post-entry stage of the virus lifecycle will open new avenues in this endeavor.